1. Field of the Invention
The present invention relates to a sheet processing apparatus and an image forming apparatus, and particularly to a unit configured to bind sheets.
2. Description of the Related Art
Hitherto, some image forming apparatuses, such as a copying machine, a laser beam printer, a facsimile machine, and a multifunction device having functions of these machines, have included a sheet processing apparatus that performs a process of, for example, binding sheets on which an image has been formed. Significant emphasis is placed on recyclability in consideration of the environment and the like, and a sheet processing apparatus has been suggested in which sheets are bound without using staples. As such a sheet processing apparatus, for example, a sheet processing apparatus is provided in which a sheet binding unit including inverted V-shaped upper teeth and V-shaped lower teeth performs a binding process on a sheet bundle.
In the sheet processing apparatus, sheets are put together and aligned, and then the sheets are pressed by meshing the lower teeth and the upper teeth so as to form, on part of a sheet bundle, projections and depressions in a thickness direction, thereby entangling fibers of superimposed sheets in the sheet bundle with each other so as to bind the sheet bundle. Hereinafter, such a binding method for binding a bundle of fibrous sheets without using staples is called stapleless binding.
Hitherto, there has been provided a sheet processing apparatus in which a cam is used as a component configured to mesh lower teeth and upper teeth (see Japanese Patent Laid-Open No. 2010-189101). In a sheet binding unit of this sheet processing apparatus, as illustrated in FIG. 10A, a cam 116 having cam surfaces 116a, 116b, and 116c that are different in length in a radial direction with respect to a rotating shaft 117 is used.
When stapleless binding is performed, the cam 116 is rotated, and upper teeth 112 disposed in an upper supporting base 110 are pressed against lower teeth 111 disposed in a lower supporting base 119 via an elastic member 115.
The cam 116 is provided with a plurality of cam surfaces 116a, 116b, and 116c so that a pressing force corresponding to the thickness of a sheet to be bound or the number of sheets to be bound is obtained. When configuration is made so that the upper teeth 112 are pressed via the elastic member 115, even in the case of a sheet bundle S having an intermediate thickness that is not able to be dealt with by the cam surface 116a, 116b, or 116c, a pressing force corresponding to the sheet bundle S may be obtained owing to deformation of the elastic member 115.
In the configuration illustrated in FIGS. 10A and 10B, in order to withstand a large force applied to the elastic member 115 when the upper teeth 112 are pressed against the lower teeth 111, an elastic member having a high spring constant is required, thereby resulting in an increase in cost.